Mammalian cell lines, such as Chinese hamster ovary (CHO) cell lines, are often used for the production of recombinant proteins. In such methods, it is desirable to generate stable cell lines and to be able to generate such high-producing stable cell lines in a relatively short period of time. The generation of such cell lines enables the rapid production of quantities of recombinant protein on a scale useful for purposes of biological evaluation and commercial production.